1. Field of the invention
The present invention relates to a display device for displaying at least one natural moving picture and a graphic picture including one or more characters used in such a picture information retrieval system by a computer.
2. Description of the prior art
An example of a conventional display device of the above kind is shown in FIG. 1, in which element 1 is a CPU; element 2 is an RBG separation circuit; element 3 is an A/D converter for converting the analog RBG signal output from the RBG separation circuit 2 to digital signals; 4 is asynchronizing signal separation circuit; element 5 is a master clock generation circuit; element 6 is a natural picture memory for storing natural picture information inputted through the NTSC terminal; element 7 is a graphic memory for storing graphic pictures or graphic images coming from CPU 1; element 8 is a display circuit for reading the picture data stored in the graphic memory 71 element 9 is a display color designating register for setting desired colors of the natural pictures to be displayed, the above, colors being selected from colors contained in the graphic pictures; element 10 is a selector switch for selecting picture data stored in the natural picture memory 6 and the graphic memory 7 in response to the output of a comparator 12 for comparing the data of the natural picture memory 6 and the data of the color designating register 9; element 11 is a D/A converter; element 13 is a display unit such as a CRT for displaying the picture output from the D/A converter 11.
In the above arrangement, the color designation area is depicted in the graphic memory 7 using the designated color values by the CPU 1. The values of the respective designated colors representing the colors for displaying the natural picture are set in the display color designating register 9 by the CPU 1.
The various characters and the graphic pictures stored in the graphic memory 7 and the natural picture stored in the natural picture memory 6 are respectively read out by CPU 1 in synchronism with the raster scanning of the display circuit 8 and the value read out from the graphic memory 7 is compared with the value read out from the color designating register 9 in the comparator 12. When the area of designated color is scanned, the switch 10 is switched towards the natural picture memory 6 side, and the output of the natural picture memory 6 is fed to the display unit 13, thereby displaying the natural picture so that the display unit 13 can display pictures containing the graphic picture with one or more characters and the natural picture.
However, in the conventional device mentioned above, only one moving picture can be displayed in one picture frame, despite the fact that the natural picture can be displayed with the graphic picture.